The DVD "Dissection of the Brain" and Spinal Cord is a great preparation for the Brain 3 class. Please pay speacial attention to chapter 13 "cerebellum" to facilitate your experience.
Be sure you understand the following words and, as applicable, know precisely where these structures are located in the body. For this class it is more important to know their 3-dimensional location and relationship with one another, than their classically described physiology.
We will go over the vestibular and cochlear systems, the three layer cortex (hippocampus and cerebellum)
Be aware of the complex subdivisions of the cerebellum:
THREE LOBES: Anterior Lobe, Posterior Lobe, Flocculo-Nodular Lobe.
VERMIS (LLCC): Lingula, Central Lobule (Lobulus Centralis), Culmen, Declive, Folium, Tuber, Pyramis, Uvula, Nodule.
LOBULES & FISSURES: Quadrangular (Superior Quadrangular) Lobule, Simplex (Inferior Quadrangular) Lobule, Posterior Superior Fissure - Superior Semilunar (or Crus I or Ansiform) Lobule, Horizontal Fissure, Inferior Semilunar (or Crus II or Ansiform) Lobule, Gracilis Lobule, Biventral Lobule, Secondary Fissure (Retrotonsillar), Tonsils of the Cerebellum
Superior olive, inferior colliculi, medial geniculate, hippocampus layers, dentate gyrus, fimbria, part of the cerebellum, autonomic innervation, sympathetic and parasympathetic nervous system, pre and post-ganglionic (synaptic) neurons, enteric nervous system, sympathetic ganglia, intermediolateral cell column, paravertebral ganglion, superior, middle and inferior cervical ganglion, stellate ganglion, sympathetic plexi, celiac plexus, superior and inferior mesenteric ganglia, aorticorenal ganglia, greater splanchnic nerves.
Please read the autonomic nervous system text below, especially the organization of the sympathetic system.
Be familiar with the brain structures from each of the following pages of "Netter's Atlas of Human Neuroscience" 1st Edition (2nd Edition in parenthesis):
Page 30 (page 47): Hippocampus, dentate gyrus
Page 32 (page 50): Hippocampus, fimbria
Page 35 (page 54-55): Posterolateral View: Pineal, superior and inferior colliculi, medial and lateral geniculate, Pulvinar, olive, vestibular area
Page 36 (page 56-57): It would be very helpful to study every word related to the cerebellum found on these pages.
Page 116 to 120 (page 172-176): Autonomic innervations
Page 121-122 (page 177-178): Cervical sympathetic ganglia
Page 126 (page 185): Sympathetic innervation, stellate ganglion
Page 129 (page 188): Sympathetic plexi, celiac plexus, superior and inferior mesenteric ganglia, aorticorenal ganglia, hypogastric plexi
Page 132 (page 195): Enteric nervous system
Page 136 (page 201): Autonomic innervations
Page 141 (page 208): Intermediolateral cell column
Page 152-153 (page 224-227): Vestibular and cochlear nuclei
Page 158 (page 235-236): Vestibular and cochlear nuclei
Page 163 (page 245): Vestibular and cochlear nuclei
Page 173 (page 255): Cerebellar lobes and regions
Page 174 (page 256): All divisions of vermix
Page 224-225 (page 336-337): Vestibular and cochlear system
Page 226 to 229 (page 338-342): Cochlear cochlear system
Page 230-231 (page 343-344): Vestibular system and pathways
Page 247 (page 368-369): Vestibular pathways
Page 253 (page 375): Cerebellar regions
Page 254 (page 376): Three layers of cerebellum
Page 257-258 (page 379-380): Vestibular and cochlear nuclei
Page 289-290 (page 414-415): Hippocampus, dentate gyrus, fimbria
"Netter's Atlas of Human Neuroscience", Icon Learning System
"Atlas of Anatomy", Thieme, Head and Neuroanatomy, ISBN: 978-1-58890-441-6
"Color Atlas of Human Anatomy, Vol. 3, Nervous System and Sensory Organs", Thieme, ISBN: 978-1-58890-0647
"Neuroanatomy, 3-D Stereoscopic Atlas", M. Hirsch, T. Kramer, Springer Ed, ISBN: 3-540-65998-6
"The Human Brain", John Nolte, Mosby, ISBN: 978-0-323-01320-8
"Neuroanatomy, Text and Atlas", John Martin, Appleton & Lange Ed ISBN: 0-8385-6694-4
Autonomic Nervous System: Review
It is important to study the information below and have an appreciation of the Somatic and Autonomic (Vegetative) Nervous System
I. The Somatic and Autonomic Nervous System (ANS)
The somatic nervous system is a voluntary system that allows us to consciously interact with our environment. It has one simple action: causing contraction of skeletal muscles. It has one fast, myelinated motor neuron outside of the central nervous system (CNS) and no ganglia. It has one neurotransmitter: acetylcholine, always activating its effector.
The autonomic nervous system (ANS) is a system of information not under direct voluntary control. The word "autonomic" comes from two Greek words that mean "self" and "law".
The ANS allows the body to respond involuntarily, subconsciously, and automatically to the body's demands for daily adjustments and maintenance of homeostasis/allostasis.
The ANS has 2 simple, mainly involuntary actions to maintain internal environment:
Contraction of smooth muscles (viscera, eyes, blood vessels, etc.) and cardiac muscles
Glandular secretion (adrenal, lacrimal, salivary, digestive, cutaneous, etc.)
The ANS is also called the general visceral motor system.
The information received by the ANS primarily comes from the surface of the body (somatic sensory), the viscera (visceral sensory), and the external environment (special sensory). The amount of sensory receptors in the viscera is 10% of the number of receptors of the skin.
Two divisions have traditionally been associated with the ANS: the parasympathetic and sympathetic nervous systems. They harmonize and counteract each other. Under normal conditions the two main branches of the ANS are usually in balance.
A third division, the *benteric nervous system*p, deals with the diffuse visceral (especially enteric) sensory input, has more recently been isolated (Michael Gershon, Columbia University).
As we saw previously, the somatic nervous system is located outside of the central nervous system (CNS). It is mainly a one-neuron system outside of the CNS (synapse spinal cord-voluntary muscle).
The ANS is comprised of at least 2 systems (sympathetic and parasympathetic) and 2 neurons outside of the central nervous system that synapse together.
The 2 neurons outside of the CNS are called the pre- and postganglionic neurons. This added interneuron gives the ANS its autonomy and capacity to make local "decision". Our practice will be to localize and work on these groups of local/regional/central control centers (GCC).
We will call the first group of ANS control centers (GCC) group "0". GCC 0 is a CNS grouping of cortical and subcortical centers responsible for the central control of the ANS.
The GCC 0 is comprised of:
ANS main hypothalamic nuclei centers:
ANS main thalamic nuclei centers:
The traditional description of the system is that preganglionic sympathetic and parasympathetic neurons use acetylcholine (ACh) type nicotinamic as their main neurotransmitter.
Postganglionic sympathetic neurons use mainly adrenaline/noradrenaline (NA). Postganglionic parasympathetic neurons use mainly acetylcholine type muscarinic (M). Stomach acid secretion is mediated by M1, cardiac manifestations by M2; most other visceral parasympathetic neurons are mediated by M3 receptors.
These simple notions are been slowly replaced by the concept of co-transmitters (multiple neurotransmitters in one synapse) and neuromodulators (they are released, but have no direct action on the postjunctional receptors). Such substances include: dopamine, ATP, nitric oxide, Peptide Y, VIP, substance P, etc.
Most organs have a dual innervation (sympathetic and parasympathetic), the main exceptions being:
1. Organs with only parasympathetic nervous system innervation:
The bronchi (no sympathetic innervation, but adrenaline in bloodstream can have a similar effect)
The lacrimal gland (no sympathetic innervation)
2. Organs with only sympathetic nervous system (SNS) innervation:
The blood vessels. All arteries and veins of any size have an exclusive sympathetic innervation
The adrenal medulla (epinephrine/adrenaline)
The sweat glands (acetylcholine)
The hair follicles
Note that superior limbs, inferior limbs and body walls have no direct parasympathetic innervation.
II. Embryology of the ANS
All of the ANS derive embryologically from the neural crests.
Neural crests are structures located on the superior-lateral aspect of the neural tube. Neural crest differentiation began mainly in the cranial region at the stage of the neural fold. They have been referred to as the fourth germ layer. Later on, three regions of the neural tube generated neural crests: rhombencephalon, mesencephalon, and prosencephalon, each with a different migratory pattern. They migrated throughout the embryo acting as agents bearing information that would modify target tissues and form many of the structures of the embryo. Numerous structures are derived from neural crests, such as:
Sympathetic plexuses: celiac, mesenteric, renal
Adrenal medulla (chromaffin cells)
Most of the ocular globe
Connective tissue around eye
C cells of thyroid gland
Cartilage rudiments (nose, face, middle ear)
Smooth muscle and adipose tissue
Odontoblast of the teeth
III. Structure and Function of the ANS
Parasympathetic Function - "The Craniosacral Division": "Rest & Digest"
Anabolic system, the parasympathetic system conserves and helps restore body energy resources. It helps regenerate injured tissues and stimulates immune functions.
It is generally most active during sleep and deep relaxation states.
Each individual parasympathetic pathway is regulated independently. The ratio of preganglionic to postganglionic neurons is 1:1 (except vagus nerve).
Parasympathetic activation is more local than sympathetic activation.
A. Effects of parasympathetic stimulation:
Decreases heart rate (M2)
Decreases respiratory rate
Decreases blood pressure
Increases blood flow to skin
Increases gastrointestinal motility, kidney function (M3)
Increases secretion of lacrimal glands (M3)
Increases salivary glands, watery secretion (M3)
Increases digestive glands
Increases gastric acid secretion (M1)
Increases bronchial glands
Constricts bronchioles (M3)
Relaxes sphincters (M3)
Contracts pupils (miosis)
Contracts ciliary muscles (accommodation) (M3)
Contracts urinary bladder (M3)
Stimulates erection (M3)
No parasympathetic innervation of the limbs, body wall, blood vessels (except a possible innervation of the coronary arteries of the heart), the sweat glands, the hair follicles and the adrenal medulla.
B. Anatomy of the Parasympathetic System:
The parasympathetic system innervates the cranium, neck, thorax and abdomen, but not the extremities.
Preganglionic parasympathetic nerves are very long and are thinly myelinated (peripheral nerve type B).
Pre-synaptic neurons: hypothalamus, brainstem and sacral segments of the spine.
Pre-synaptic neurotransmitter: Acetylcholine
Pre-ganglionic neurons are in cranial nerves III, VII, IX, X and in the lateral horn of sacral segments S2, S3, S4 (splanchnic nerves)
Postganglionic nerves are typically short and are unmyelinated (type C or IV). Fibers usually synapse close to or within the organ they innervate. They can use the same nerve plexus as the sympathetic system.
Usually the ratio of preganglionic to postganglionic fibers is 1:1 (except for the vagus nerve). The parasympathetic system has little "divergence".
C. Specific Anatomy of the Parasympathetic System:
1. Cranial Division
The cranial nerves nuclei include:
Edinger-Westphal nucleus (III)
Superior salivatory nucleus (VII)
Inferior salivatory nucleus (IX)
Two nuclei of the vagus (X): dorsal motor nucleus and nucleus ambiguus
Parasympathetic ganglia associated with the cranial division:
Edinger-Westphal nucleus (III): ciliary ganglion for papillary constrictor muscle (iris) and ciliary muscle (lens)
Superior salivatory nucleus (VII): pterygopalatine ganglion for lacrimal and nasal glands;
Submandibular ganglion for submandibular and sublingual salivary glands
Inferior salivatory nucleus (IX): otic ganglion for the parotid gland
Two nuclei of the vagus (X):
dorsal division: palate, larynx, esophagus
ventrolateral division: heart
The vagus (cranial nerve X), one of the most important parts of the parasympathetic nervous system is a nerve approximately 80% sensory (tractus solitarius) and 20% motor. It innervates both somatic and visceral organs in the neck, chest and abdomen.
2. Sacral Division
Sacral segment S2-S4 (intermediolateral spinal cord segment S2-S3-S4) Innervate: left 1/3 transverse colon, descending colon, rectum, bladder, reproductive organs
2. Sympathetic Function - The "Thoracolumbar Division": "Fight or Flight"
Catabolic system, the sympathetic system expends body energy resources, depresses immune functions and releases epinephrine (adrenaline) and norepinephrine (noradrenaline) hormones.
The Sympathetic Nervous System is often activated as a whole.
A single preganglionic axon contacts many cells. Postganglionic axons can receive input from approximately 30 different preganglionic fibers (important) "divergence"). Sympathetic activation is usually a diffuse activation with multiple systems activated concurrently.
We are going to work mainly on the sympathetic system in this class because:
1. The sympathetic NS has more general effects (rather than local). It has more widespread effects, usually mass responses (more divergence).
2. Is more distributed to the whole body.
3. Has effects lasting relatively longer: it stimulates the medulla of adrenal glands that secrete hormones in the blood circulation.
But let's remember the parasympathetic nerves have about 3 times more sensory axons (sensations of fullness, tension, etc.), than sympathetic (usually pain messages).
Sympathetic functions are globally the reverse of parasympathetic functions.
A. Effects of sympathetic stimulation
Increases heart rate (beta á1)
Increases blood pressure
Vasoconstricts blood vessel (alpha 1)
Increases respiratory rate
Decreases blood flow to skin
Increases secretion of epinephrine
Increases secretion of sweat glands (acetylcholine)
Increases blood sugar level
Decreases gastrointestinal motility, kidney functioning
Decreases secretion of digestive glands
Constricts sphincters; causes spasm
Dilates the pupils (mydriasis) (T1, via carotid)
Stimulate fat cells via Beta 3 receptors and induces lipolysis
Pain is usually carried by sympathetic (or somatic) nerves. No sympathetic innervation of the bronchi and the lacrimal glands.
B. General Anatomy of the Sympathetic System:
Sympathetic fibers leave the spinal cord (white ramus) and usually synapse in one ganglion of the paravertebral sympathetic chain.
Most preganglionic sympathetic nerves are short and are myelinated, whereas the postganglionic nerves are long and are unmyelinated.
Each preganglionic cell gives rise to multiple fibers that innervate cells in either the paravertebral sympathetic chain, the prevertebral ganglia (i.e. celiac, aorticorenal and mesenteric), or the few terminal ganglia in the target organs (i.e. adrenal gland). Usually the ratio of preganglionic to postganglionic fibers is one to 15 or 30.
Preganglionic neurons (acetylcholine) are located in the lateral horn of T1 to L2 spinal cord segments. They innervate most of the body. Postganglionic neurons: release noradrenaline (NA) onto Alpha-1, Beta-1, Beta-2, or Beta-3 adrenergic receptors.
Exceptions, the following sympathetic structures don't release norepinephrine:
Adrenal medullary chromaffin cells secrete epinephrine
Sympathetic nerves innervating sweat glands secrete acetylcholine
Sympathetic nerves innervating blood vessels in skeletal muscle secrete acetylcholine
In some animals, there are also sympathetic cholinergic fibers that go to blood vessels supplying muscle
Sympathetic nerves innervating renal blood vessels secrete dopamine
The group of control center 1 (GCC 1) is the intermediolateral segments of the spinal cord: T1 to L2 or L3.
The group of control center 2 (GCC 2) is the sympathetic chain (paravertebral): cervical, thoracic, lumbar and sacral ganglia and 1 midline impar (coccygeal) ganglion.
Leaving only the ganglion, sympathetic neurons can bifurcate medially and innervate the viscera, laterally for the body wall (blood vessels, sweat glands, arrectors pilorum muscles) or go up or down the sympathetic chain.
Only 13 or 14 ganglia receive direct sympathetic branches (white rami) from the spinal nerve, the rest have only grey (unmyelinated) communicans, receiving nerves ascending or descending from the sympathetic chain.
1. The synapse of the sympathetic chain that innervates:
2. The synapse of the sympathetic chain innervating the head and neck is always in the paravertebral cervical chain (one of the 3 sympathetic cervical ganglia)
3. The synapse of the sympathetic chain innervating: the thorax and limbs is always in the paravertebral chain: C1-T5
4. The synapse of the sympathetic chain innervating the abdomen and pelvis is always in the preaortic (prevertebral) ganglia. This is the 3rd group of control center (GCC 3): celiac ganglion, superior mesenteric ganglion, aorticorenal ganglion, and inferior mesenteric ganglion. The postganglionic neuron will usually synapse again to a neuron of the enteric nervous system (and not directly in the organ tissue).
C. Specific Anatomy of the Sympathetic System:
GCC 2: sympathetic chain (paravertebral). There are usually 22 to 23 pairs of paravertebral ganglia: cervical, thoracic, lumbar and sacral ganglia and one midline impar (coccygeal) ganglion.
1. Principal Cervical Paravertebral Ganglia
Three cervical ganglia in front of cervical transverse processes:
A. Superior Cervical Ganglion:
Also called the ganglion of Hirschfeld, it is the largest cervical ganglion (4-5 cm in length, 1 cm in width) and is located behind the internal carotid at the level of the transverse process of C2-C3 (from C1 to the angle of the mandible). Posterior to it is the longus capitis muscle. This ganglion is usually made up of the agglomeration of four ganglia, C1 to C4.
The superior cervical ganglion mainly supplies the head and neck and the heart. It has many branches including the pharyngeal nerves, laryngeal and superior cardiac nerve. It runs superiorly to the carotid canal, "hitchhiking" along the carotid arteries and their branches, connecting with a carotid ganglion, then further to the carotid plexus, the cavernous sinus where it meets branches from cranial nerve III, IV, optic ganglion of V, VI, Tympanic nerve of IX.
B. Middle Cervical Ganglion or Thyroid Ganglion:
The smallest of the three cervical ganglia, sometimes not present. It is located at the level of the transverse process of C6 or C7. It is usually superior or close to the inferior thyroid artery. It is the coalescence of the ganglion of C5 and C6. The middle cervical ganglion mainly supplies the area of the neck and the heart. It branches into the middle cardiac nerve, the largest of the three cardiac nerves.
C. Inferior Cervical Ganglion or Stellate Ganglion:
It is about 0.8 to 1 cm in length and lies superior to the apex of the lung. It is anterior to the transverse process of C7 and the 1st rib. It is often the fusion of the ganglion of C7 with the first thoracic ganglion. It is at the level of the transverse process of C7 or T1.
The inferior cervical ganglion mainly supplies the posterior cranial arteries, lower neck, upper extremities, and the heart. It branches into the inferior cardiac nerve. The left stellate ganglion is lower than the right.
2. Thoracic and Abdominal Ganglia: Paravertebral Ganglia
Ten to twelve dorsal paravertebral ganglia: mostly in front of the head of the ribs, covered by pleura (except dorsal 11 and 12, lateral to body of vertebrae). The nerves have to pierce the diaphragm.
The 3rd group of control centers (GCC 3) are the prevertebral (preaortic) ganglia.
Principal prevertebral ganglia:
Celiac ganglion or semi lunar ganglion ("solar plexus", epigastric plexus)
Largest ganglion in the body. It is anterior to the aorta and the crura of the diaphragm.
Superior mesenteric ganglion
Inferior mesenteric ganglion
The medulla of the adrenal glands are sometimes compared to a modified sympathetic ganglia (postganglionic neurons) because there are only preganglionic fibers (T8-L1) stimulating them - no postganglionic fibers. The adrenals (suprarenal gland) weigh about 8-10 g, anterior to the body T12-L1 and rib 11 and 12th.
Adrenal glands are made of a capsule, an outside cortex (with 3 layers, zona glomerulosa for aldosterone, zona fascicularis and zona reticularis for cortisol and sexual hormones) and the medulla in the center for the catecholamines: epinephrine (adrenaline) and norepinephrine (noradrenaline).
The medulla of the adrenal glands is also part of GCC 3.
The chromaffin cells in the medulla, the center of the adrenal glands, secrete the catecholamines: epinephrine (adrenaline) and norepinephrine (noradrenaline).
The greater splanchnic nerve (T5-T10) innervate the medulla of the adrenal glands and stimulate directly (preganglionic fibers) its chromatofinn cells that release approximately 80% of adrenaline and 20% of noradrenaline into the blood. Note that this percentage is inversed for the CNS, where the locus ceruleus releases 80% of noradrenaline.
The medulla of the adrenal glands is the only place where the body can convert norepinephrine to epinephrine. Epinephrine is secreted into the blood stream, so its effects are similar to norepinephrine. Epinephrine effects last about 10 times longer.
Tyrosine convert to Dopa
Dopa to Dopamine
Dopamine to norepinephrine, then to epinephrine in the adrenal glands
3. Lumbo-Pelvic Ganglia: Paravertebral Ganglia
In abdomen and pelvis prevertebral ganglia are near the ventral surface of the vertebral column.
Four lumbar ganglia anterior or lateral to body of the vertebrae
Three to five sacral ganglia and the impar (meaning unpaired) or coccygeal ganglion, all in front of the sacrum, medial to the anterior sacral foramina. The impar ganglion is usually 3-4 mm in diameter, located anterior to the last coccygeal vertebrae. It may have a nervous and a neurocrine function.
Some fibers going to the abdominopelvic area can synapse in a prevertebral ganglion located close the abdominal aorta or branches (splanchnic nerves).
The splanchnic nerves are presynaptic nerves, having a synapse in the GCC 3 that contribute to visceral innervation.
Main splanchnic nerves:
Greater splanchnic nerve-spinal level origin: T5 through T8, T9, or T10 (to celiac ganglia)
Lesser splanchnic nerve (94%)-spinal level origin: T9 through T10 or T11 (to superior
Lower (least) splanchnic nerve (56%)-spinal level origin: T12 (to renal ganglia)
Sacral splanchnic nerves
The ganglia and fibers make a number of ANS plexi:
Renal plexus and superior Mesenteric plexus
Inferior Mesenteric plexus
Hypogastric (pelvic) plexus
Ovarian or spermatic plexus
The 4th group of control centers (GCC 4) could be almost anywhere (anatomical variations). Usually close to known ganglion, or close to arteries or groups of lymph nodes (high innervation)
3. The Diffuse Visceral (Enteric) Nervous System
All viscera are innervated by the sympathetic and parasympathetic system.
The enteric nervous system includes as many as one billion neurons, 1/100th of the number of neurons in the brain, and much more than the number of neurons in the spinal cord.
There are two main layers of neurons throughout the wall of the intestines and act independently of sympathetic and parasympathetic innervation:
External Plexus: Myenteric Plexus of Auerbach. It is located between the inner circular muscle layer and the outer longitudinal muscle layer. This plexus is responsible for most smooth muscles movements (peristalsis) of the intestines.
Inner Plexus: Submucosal Plexus of Meissner (absent in the stomach and esophagus). It is responsible for sensing the environment of the intestines and regulating it response (vascularization, cell metabolism, ion and water transport).
Depending on conditions, they can be either excitatory or inhibitory.
There are numerous glial cells in the enteric nervous system, as well as the interstitial cell of Cajal (ICC). This cell is not neural or glial, but somehow in between, it acts as the intrinsic pacemaker of the bowel.
GCC 0: CNS cortical and subcortical centers including reticular formation, hypothalamus, pituitary, etc.
GCC 1: The intermediolateral segments of the spinal cord: T1 to L2 or L3.
GCC 2: Sympathetic chain (paravertebral). 22 to 23 pairs of paravertebral ganglia: cervical, thoracic, lumbar and sacral ganglia and 1 midline impar (coccygeal) ganglion.
GCC 3: Preaortic (prevertebral) ganglia: celiac ganglion, superior mesenteric ganglion, aorticorenal ganglion, inferior mesenteric ganglion + adrenal medulla.
GCC 4: They could be almost anywhere (anatomical variations). Usually close to known ganglion, or close to arteries or groups of lymph nodes (high innervation).